Expanded polystyrene (EPS) is a rigid and tough, closed-cell foam. It is usually white and made of pre-expanded polystyrene beads. EPS is used for disposable trays, plates, bowls and cups; and for carry-out food packaging and refrigerant containers, as it has good insulating properties. Other uses include molded sheets for building insulation and roofing materials, and packing material (“peanuts”) for cushioning fragile items inside boxes. Sheets are commonly packaged as rigid panels (generally sized as 4 by 8 or 2 by 8 feet in the United States), which are also known as “bead-boards.”
There are two basic processes of polymerizing EPS. Suspension polymerization involves use of a blowing agent (typically pentane) which is used to generate the cells which enhance the insulating properties. But pentane is undesirable for the environment, because, like other organic solvents, exposure to it is associated with toxicity to the nervous system, reproductive damage, liver and kidney damage, respiratory impairment, cancer, and dermatitis.
A polymerization process which reduces the amount of pentane required to generate a product with desired insulating properties is desirable to reduce the exposure of workers to it, and to reduce the release of pentane into the environment. Following production of EPS, it can be molded or extruded into desired shapes and forms.